Quantum mechanics and biology
You probably know many examples of how the microscopic laws of quantum physics make their presence felt in our macroscopic world: lasers (spontaneous emission), semiconductors (energy band gap), atomic clocks, etc.
But here is something different (not new to science, just a new realization for me): a simple example of how the impact of quantum mechanics can be seen in biology and all of life.
As explained by quantum physics (versus classical physics), the atomic orbitals of the hydrogen atom (the spatial, non-spin part of the energy eigenstates for a single proton plus a single electron) have shapes that are spherical (s orbitals) or with various lobes (p orbitals, d orbitals, etc.).
Beyond hydrogen, for more complex atoms such as carbon and nitrogen with larger nuclei and more electrons, the details get much more complex, but the same basic pattern holds with atomic orbitals that are s, p, d, etc.
These nonspherical atomic orbitals such as p orbitals contribute to covalent bonds such as double bonds that prevent rotation around the bond, for example in the peptide bond between a N and a C. In other words, there is a certain degree of rigidity in the peptide bond.
As with everything in life, it’s not good to have no structure at all, but it’s also not good to have too much structure. And so the rigidity in the peptide bond is extremely important because it imposes just the right amount of structure on the possible shapes of a protein. And the structure of proteins is what enables all of the machinery of life.
So to reiterate, a C and a N can form a peptide bond that is not cylindrically symmetric and does not permit free rotation around the bond axis, as a direct consequence of quantum mechanics.
A fun example of how quantum mechanics has a simple and specific impact on the structure of proteins, and therefore on all of biology!